Chapter 25 The Skin

The Skin: More than a Mechanical Barrier• Squamous epithelial cells• Melanocytes• Dendritic cells• Lymphocytes• Neural end organs and axonal processes• Adnexal components• Sweat glands• Hair follicles

• Definitions of Macroscopic Terms• Definitions of microscopic Terms

Definition of Macroscopic Terms

Excoriation Traumatic lesion breaking the epidermis and causing a raw

linear area( deep scratch): often self-induced

Lichenification Thickened and rough skin characterized by

prominent skin markings: usually the result of repeated rubbing

Definition of Macroscopic terms

Macule Circumscribed lesion, 5mm or smaller in diameter

characterized by flatness and distinguished by coloration (patch is greater than 5 mm)

Onycholysis Separation of nail plate from nail bed

Definition of Macroscopic Terms

Papule Elevated dome-shaped or flat-topped lesion 5 mm or

less across ( nodule is greater than

5mm)Plaque Elevated flat-topped lesion,

usually greater than 5mm across ( may be caused

by coalescent papules)

Definition of Macroscopic Terms

Pustule Discrete, pus-filled, raised lesion

Scale Dry, horny, platelike excrescence: usually

the result of imperfect cornification

Definition of Macroscopic Terms

Vesicle Fluid-filled raised lesion 5mm or less across ( Bulla is greater

than 5mm. Blister is the common term

for both)

Wheal Itchy, transient, elevated lesion with variable blanching

and erythema formed as a result of dermal edema

Definition of Microscopic Terms

Acantholysis Loss of intercellular cohesion between keratinocytes

Acanthosis Diffuse epidermal hyperplasia

Dyskeratosis Abnormal, premature keratinization within cells

below the stratum granulosum

Definition of Microscopic Terms

Erosion Discontinuity of the skin showing incomplete loss of the epidermis

Exocytosis Infiltration of the epidermis by inflammatory cells

Hydropic swelling Intracellular edema of(Ballooning) keratinocytes, often seen

in viral infections

Definition of Microscopic Terms

Hypergranulosis Hyperplasia of the stratum

granulosum, often due to

intense rubbing

Hyperkeratosis Thickening of the stratum

corneum, often associated

with a qualitative abnormality of keratin

Definition of Microscopic Terms

Lentiginous A linear pattern of melanocyte proliferation within the epidermal basal cell layer

Papillomatosis Surface elevation caused by hyperplasia and enlargement of contiguous dermal papillae

Parakeratosis Keratinization with retained nuclei in the stratum corneum. On mucous membranes parakeratosis is normal.

Definition of Microscopic Terms

Spongiosis Intercellular edema of the epidermis

Ulceration Discontinuity of the skin showing complete loss of the epidermis revealing dermis or subcutis

Vacuolization Formation of vacuoles within or adjacent to cells; often refers to basal cell- basement membrane zone area

Disorders of Pigmentation and Melanocytes• Freckle (Ephelis)• Lentigo• Melanocytic nevus (pigmented nevus, mole)

• Junctional nevi -> compound nevi -> intradermal nevi• Maturation

• Dysplastic nevi• Precursors of melanoma

• Melanoma• Radial growth ( horizontal ) vs vertical growth• Inherited genes and sun exposure• ABCs of melanoma• Prognostic factors

• Tumor depth• Number of mitoses• Tumor regression• Tumor infiltrating lymphocytes• Gender• Location

Benign Epithelial Tumors• Seborrheic keratoses• Acanthosis nigricans – DM, malignancy• Fibroephithelial polyp – skin tag• Epithelial cyst (wen)• Adnexal (appendage) tumors

Premalignant and Malignant Epidermal Tumors• Actinic keratosis• Squamous cell carcinoma – nodular, scaley, may ulcerate• Basal cell carcinoma – pearly papules, prominent

telangiectasias• Sun exposure and DNA damage

Tumors of the Dermis• Benign fibrous histiocytoma (dermatofibroma)• Dermatofibrosarcoma proturberans

Tumors of Cellular Migrants to the Skin• Mycosis fungoides (cutaneous T cell lymphoma)• Sezary-Lutzner cells

• Mastocytosis• Mast cell degranulation• Darier sign , dermatographism

Disorders of Epidermal Maturation

• Icthyosis• Defective desquamation• Impaired epidermal maturation

Acute Inflammatory Dermatoses• Urticaria – hives• Wheal and flare• IgE mediated – Type I hypersensitivity

• Acute eczematous dermatitis• Allergic contact dermatitis• Atopic dermatitis• Drug-related eczematous dermatitis• Photoeczematous dermatitis• Primary irritant dermatitis

• Erythema multiforme• Infections, drugs, collagen vascular diseases

• Macules, papaules, vesicle, bullae, target lesions• Steven-Johnson syndrome – erosions of skin and mucous membranes,

toxic epidermal necrolysis

Chronic Inflammatory Dermatoses• Psoriasis• Well-demarcated pink to salmon-coored plaques with silver-white

scale• Arthritis, myopathy, enteropathy, spondylitic joint disease, AIDS• Elbows, knees, scalp, lumbosacral areas, intergluteal cleft, glans

penis• Nail changes• Pustular psoriasis• HLA-C

• Seborrheic dermatitis• Scalp, forehead, face, presternal area• Leiner disease, cradle cap, HIV, Parkinson disease, sebum, yeast

• Lichen Planus – pruritic, purple, polygonal, planar papules, plaques

Blistering (Bullous) Diseases• Inflammatory Blistering Disorders• Pemphigus

• Autoantibodies that result in dissolution of intracellular attachments within the epidermis and mucosal epithelium

• Acantholysis

• Bullous pemphigoid• Subepidermal, nonacantholytic blisters• Linear deposition of immunoglobulin and complement in the

basement membrane zone

• Dermatitis herpetiformis• Urticaria and grouped vesicles, celiac disease, symmetric extensor

surfaces

• Noninflammatory Blistering Disorders• Epidermolysis Bullosa and Porphyria

Disorders of Epidermal Appendages• Acne vulgaris• Noninflammatory – open and closed comedones• Inflammatory – papules, nodules,pustules• Propionibacterium acnes• Androgens

• Rosacea• Inappropriate activation of the innate immune system

Panniculitis• Erythema nodusum and erythema induratum

Infection• Verrucae (warts) - HPV• Molluscum contagiosum – pox virus, umbilicated lesions• Impetigo – strep and staph, honey-colored crust• Superficial fungal infections – tinea capitis, barbae, corporis,

cruris, pedis, onychomycosis, dermatophytes; versicolor - yeast